Process of making photographic emulsions



Patented Feb. 9, 1932 UNITED STATES PATENT entice RAYMQNID H. LAMBERT,OF ROCHESTER; NEW YORK, ASSIGNUR T0 EASTMAN KGDAK GOMIPAINY, OFROCHESTER, NEW YORK, A GORPDJBLATION Old" NEW YORK PROCESS OF MAKINGPHOTOGJR-APHIC EMULSION$ lt'o Drawing.

This invention relates to a process for the manufacture of photographicemulsion and particularly to a method of Washing the emulsion.

In the preparation of a photographic light-sensitive emulsion thesensitive substance is usually silver halide. This material is preparedby addition of a soluble silver salt to a soluble halide such aspotassium or ammonium halide. In the resulting double decomposition orchemical interchange, one product is the insoluble silver halide. Itsstability and sensitivity are largely controlled by the presence oi.some protective colloid, usually gelatine, during the precipitation ofthe insoluble silver halide. A stable suspension is-thus formed.

There are likewise formed in this reaction soluble inorganic salts thatmust 'be removed from the gelatine prior to further treatment andcoating it upon photographic plates or film. Many methods for washingout these superfluous salts have been developed since the processes ofKing and Johnson developed in 1873. In some processes the set gelatinesuspension is extruded or cut into fine shreds and then subjected to awashing treatment which may last from 2% to IE5 hours. The prior methodshave been eumhersome, slow and therefore ineflieient.

It is the object ot the present invention to provide a method which willovercome many of the disadvantages of the former processes for washingand purifying the gelatine suspension.

I have found that it suitable inorganic salts be added to thephotographic emulsion,

the gelatine may be coagulated therefrom and will settle to thebottom ofthe container.

- In settling the gelatine will carry with it substantially all of thesilver halide which has been formed in the emulsion, and of coursesomeot' the soluble salts which are formed by the interaction of the silversalt With the alkaline halide. The gelatine is in such a form that itmay be readily andeasily washed free from the soluble salts without thenecessity of shredding or extruding that has hitherto been used.

The inorganic salts which I have tound 7 Application filed April 19,

to the increase 1929. Serial No. 356,607.

suitable for this purpose are the salt-forming elements of the IV groupot the Periodic Tfable, such for example as tin, lead, titan um, cerium,thorium, zirconium, germanium, etc. I have found that the nitrates ofthese elements are most suitable for my purpose. patihle with theemulsion without in any.

Other salts, however, that are comway afiecting the sensitivity ot thecoating thatmay result may be used.

It is essential that the salt be used in the correct concentration. Toosmall an amount of the salt results in the coagulation oft e gelatine ina slimy relatively non-viscous mass; while too great a concentration ofthe salt results in a rubbery, tough material trom wllich it is verydifficult to wash the soluble sa s.

' tion or settling of the-gelatine requires from two to 7 four hours.Temperatures much above room temperatures should be avoided, as thesettling of the gelatine therefrom is considerably retarded in directproportion in temperature of the emulsion.

sired form it carries down with it substantially all of the silverhalide whichhas been formed in the gelatine solution or emulsion.

Two or three trials will be sufficient to determine the most desirableconcentra tion. In the use of thorium nitrate, rm: eX-

When the gelatine has eoagulated in the de- I The liquid above thecoagulated gelatine contains a large proportion of the soluble saltwhich liquid can be readily decanted. The gelatine material remainingmay he very easily washed, as Water difiuses very readily throughout themass. In case any fiocculent gelatine remains above the settled gelatinelayer, it can be readily separated from the supernatent liquid by simplefiltration and can be as readily washed as the main gelatine layer. 1

The concentration of the gelatine in the solution is not critical, but Ihave found that gelatine solutions containingv as little as from 0.51%of elatine may be readilycoagulated by my method. In fact, the gelatinecoagulated fromsuch a solution washes more easily and water difi'usesmore readily through it than it does through a 5% gelatine which hasbeen allowed to set and has been shredded into fine noodles.

The supernatant liquid contains a. large proportion of the soluble saltsand in a con-' centration sufliciently great to permit their recoverytherefrom to be economically effected. Heretofore there has been littleor no recovery of the salts which have been washed from the emulsion dueto the cost of concentrating and recrystallizing from the diluteliquors. My procedure makes this operation economically practical due tothe high percentage of salts found especially in the decanted layer.

After a thorough washing of the gelatine a slight addition of water maybe made to the jelly-like mass, and by heating to 60 or 70 C. thematerial will readily deflocculate.

' The temperature of defiocculation depends volume of the emulsion is800-900 cc., when,

upon the concentration of the coagulating salt used. At this point moregelatine ma be added and the emulsion digested as wil be well known tothose expert in the art.

I will now describe a specific example of carrying out my method ofcoagulation and washing of the gelatine emulsion, but it will beunderstood that I shall not be restricted thereby except as indicated inthe appended claims. Two liters of a prepared emulsion containing 20grams of gelatine and the pre-- cipitated silver halide in suspensionare added with constant stirring to two liters of a solution containing2 grams of thorium nis trate. The gelatine containing substantially allthe silver halide or other suspended insoluble matter settles to thebottom of the container in about 2 to 4 hours at a temperature of 10-20C. The mother liquor is decanted and the gelatine layer washed withdistilled water until substantially all the soluble salts are removedfrom it. This subsequent washing is carried out at room tem perature orlower. After washing the coagulum is heated to 60 or C. then 30 grams ofgelatine in about 200 cc. of water are added while stirring. An emulsionwill slowly reform. Water is then added until the final the material isobtained which coats smoothly on a support such as glass or film base.

Such material, when coated on a plate, dries without staining, bumps, orchecking, so often found on photographic plates. I have also noted thatplates so obtained have more speed, fix more rapidly, and wash morequickl than ordinary plates. Plates unexposure and development an imageis obtained which is remarkably clear and with good detail. The presenceof these salts likewise acts as a hardener, and the usual hardeners suchas alum, formalin, or alcohol need not be used with an emulsion preparedin this way.

Various changes and modifications may be made in the manner of carryingout this process and equivalents of the coagulating salt used without inany way departing from this invention or sacrificing any of theadvantages derived therefrom.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver halide, the step whichcomprises coagulating the gelatine,

2. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver halide, the

step which comprises coagulating gelatine,

with occluded silver halide, with a soluble salt of thorium.

3. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver halide, the step whichcomprises coagulating gelatine, with occluded silver halide, withthorium nitrate.

4. In the process of reparing. gelatino silver halide emulsions, t estep which comprises coagulating a dilute aqueous gelatinosilverhalide-containing emulsion with a soluble salt of an element of the IVgroup of the Periodic Table.

5. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver halide, the step whichcomprises coagulating the gelatine, with occluded silver halide, withapproximately 5 to 20 parts of thorium nitrate for every 100 parts ofgelatine present.

-6. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver halide, the step whichcomprises coagulating the gelatine, with occluded silver halide, at atemperature of 10 to 20 C. with approximately 5 to 20 parts of thoriumnitrate.

7. In the process of preparin a light-sensitive gelatino silver halideemu sion, the step which comprises adding a soluble salt of an elementof the IV group of the Periodic Table to the emulsion therebycoagulating the gelatine and occluding therewith substantially all thesilver halide contained in the emulsion. I

8. In the process of preparing a gelatine silver halide emulsion, thestep which comprises adding a soluble salt of an element of the IV groupof the Periodic Table to the emulsion, allowing the gelatine, withoccluded silver halide, to settle and washing itfree from soluble salts.

9. In the process of preparing a gelatino silver halide emulsion, thestep which comprises adding a soluble salt of an element or the IV groupof the Periodic Table to the emulsion, allowing the gelatine, withoceluded silver halide, to settle and decanting V the mother liquor. v

10. In the process of preparing a gelatino silver halide emulsion, thestep which comprises adding a soluble salt of an element of the IV groupof the Periodic Table to the emulsion, allowin the gelatine, withoceluded silver halide, to settle and decanting the mother liquor, andfinallyrecovering the soluble salts from the mother liquor.

11. In the process of preparing a lightsensitive gelatino silver halideemulsion from an emulsion containing gelatine and a silver halide, thestep which comprises adding'to the emulsion 5% to 20% (by weight of thegelatine present) of thorium nitrate at a temperature of 10 C. to 20 0.,allowing the gelatine, with occluded silverhalide, to settle,

decanting the mother liquor and washing the coagulated gelatinesubstantially free from soluble salts.

12. In the process of preparing gelatino silver halide emulsions from anemulsion containing gelatine and a silver .halide, the step whichcomprises coagulating the gelatine,

with occluded silver halide, with a soluble salt of an element of the IVgroup of the Periodic Table, washing the gelatlne, adding a small amountof water and the required addition of gelatine, and heating to reform anemulsion.

13. In the process of preparing gelatine emulsions from an emulsioncontaining gelatine and insoluble suspended matter, the step whichcomprises, coagulating the gelatine,

with occluded insoluble suspended matter, with a soluble salt of anelement of the IV group of the Periodic Table. j

14. In the process of preparing gelatine light sensitive emulsions froman emulsion containing gelatine and insoluble suspended light-sensitivematter, the step which comprises coagulating the gelatine, with 0ccludedlight-sensitive matter, with a soluble salt of an element of the IVgroup of the Periodic Table.

Signed at Rochester, New York, this 16th day of April, 1929.

RAYMOND H. LAMBERT.

